I keep a red flag in case I get penalized

In American football, a yellow flag is thrown if there is a penalty. A red flag is thrown to challenge a referee’s decision. He uses a red flag instead of a yellow one as a reference to his gang affiliation, blood. Blood in, blood out.

Also, if one’s team is called for a penalty, the coach can challenge the call by throwing his red flag. Weezy is saying that he won’t back down to those who are attacking him.